in cng nghip trong dy chuyn sn xut nhm thanh nh hnh

ng Sng tham kho phn no ly c copy vo gio trnhin cng nghip

trong dy chuyn sn xut nhm thanh nh hnh

Li ni u

Gio trnh in cng nghip trong dy chuyn sn xut nhm thanh nh hnh c son tho nhm p ng nhu cu o to cng nhn vn hnh cc thit b sn xut nhm thanh nh hnh ca Cng ty Nhm Sng Hng. Cc thit b trong dy chuyn sn xut rt a dng, phong ph c nhiu thit b hin i tin tin, ng thi cng nhiu thit b ph thng, n gin. Vy lm sao trong mt thi gian ngn cc cng nhn c th nm bt c quy trnh vn hnh thit b v tr cng tc ca mnh? Cng nh m bo an ton trong sn xut.

p ng c nhu cu trn th gio trnh ny c son tho vi phng chm a ra cc nguyn l, mch in c bn nht, dng nhiu nht trong thc t - r rng, ngn gn cho mi ngi u c th hiu v nm bt c (k c vi nhng ngi khng phi l cng nhn in).

Sau khi hc xong gio trnh ny, mi ngi cng nhn s:

1- Hiu c cc quy trnh, nguyn tc trong vic vn hnh, s dng cc thit b, my mc dng trong dy chuyn sn xut nhm.2- Hiu bit c bn v k thut an ton in trong sn xut cng nghip.

Mc d c tham kho nhiu ti liu v qua thc t lp t vn hnh dy chuyn thit b Cng ty. Nhng do trnh v thi gian chun b hn ch chc khng trnh khi khim khuyt. Rt mong c s ng gp hon thin ca c gi hon thin thm.

II- Mt s kin thc c bn v mch in 3 pha:

Trong sn xut cng nghip hin nay ngun in 3 pha 4 dy 380V 50Hz c s dng rt rng ri, nn ta cn phi nm c cc i lng ch yu ca n.

1- Cch to ra ngun in 3 pha:

Ngun in 3 pha c to ra bi my pht in 3 pha cc nh my sn xut in, thc cht

n l 3 dng in 1 pha

lch nhau 1 gc 1200 in.

- Mch 3 pha c cc i

lng pha v i lng

dy Uf , Ud , If , Id

- in p pha Uf : l in p gia 1 pha v dy trung tnh.

- Dng in pha If : l dng in chy trong mi pha ca ngun hoc ti.

- in p pha Ud : l in p gia 2 dy pha.

- Dng in pha Id : l dng in chy dy dn t ngun n ti.

2- Cch mc mch in 3 pha:

Mch 3 pha c hai cch mc l mc Y v mc sau y ta xt c th tng cch mc.

a/ Cch mc hnh Y: 3 im cui c ni vi nhau, cn 3 im u c ni vi 3 pha ngun.

+ Trong cch mc Y ta c:

- in p dy gp ln in p pha

Ud = . Uf- Dng in dy bng dng in pha

Id = If

b/ Cch mc hnh :

im cui pha ny c ni vi im u pha kia v ti cc im chung ni vi ngun.

- Trong cch mc ny ta c:

- in p dy bng in p pha

Ud = Uf

- Dng in dy gp ln dng in pha.

Id = . Ifc/ Cng sut mch 3 pha:

- Trong trng hp mch khng i xng th cng sut mch 3 pha bng tng cng sut ca 3 mch 1 pha.

P3f = PA + PB + PC = UfA . IfA . Cos(A + UfB . IfB . Cos(B + ...

Q3f = QA + QB + QC = ( Ufi . Ifi . Sin(i

S3f = SA + SB + SC = ( Ufi . Ifi- Vi mch 3 pha i xng ta c:

P3f = . Ud . Id . Cos(

Ud: in p dy

Q3f = . Ud . Id . Sin(

Id : Dng in dy

S3f = . Ud . Id

Cos(: Gc lch pha gia . dng v p 1 pha.

III- Cc kh c in v my in thng dng:

A- Cc kh c in thng dng:

nh ngha: Kh c in l cc thit b ng ngt, chuyn i mch in, khng ch, bo v, iu khin v kim tra s hot ng ca h thng in ngoi ra cn kim tra v iu chnh cc qu trnh khng in khc.

Sau y ta xem xt mt s kh c in thng dng.

1- Cu dao: L kh c in ng ct bng tay mch h p vi s ln ng ct nh v dng ct nh.

- C th kt hp vi cu ch bo v ngn mch.

- Khi s dng cn ch in p v dng in ti

chn cu dao cho thch hp. Vi cu dao lm

nhim v cch l hoc cng sut ti ln th

tuyt i khng c ngt cu dao khi ang c

ti nu khng s xy ra nguy him do dng h quang gy ra.

2- Cu ch: L kh c in bo v thit b v li in trnh khi dng in ngn mch hoc qu ti.

- B phn c bn ca cu ch l dy chy, n thng c lm bng cc cht c nhit nng chy thp: Ch, km, hp kim, ch thic hoc bng l ng, nhm.

- Cc dy chy thng c t trong

mt ng cch in bng s, bn trong

y cht dp h quang (ct thch anh).

- Trong thc t hay s dng cu ch ng

kiu RTO ca Trung quc vi dng in in mc 16A, 32A, 100A, 120A, 200A.

- cu ch bo v c i

tng cn bo v th mt ch

quan trng l ng c tnh

Ampe Giy (A S ) ca cu

ch phi nm di c tnh A- S

ca thit b.

- Dng in gii hn ca dy

chy cu ch, thng bng

1,15 ( 1,5 dng nh mc ca n tu theo loi cu ch.

Igh = (1,15 ( 1,5 )Im3- Nt n: L kh c in iu khin dng

ng ct mch in li h p.

- C nhiu loi nt n, thng m NO, thng

ng NC hoc c thng m, thng ng, nt

n lin n, nt n tc ng nhanh, nt n t gi...

- Khi s dng cn ch in p, dng in

nh mc ca nt n v u ng chng loi (NO, NC, L) trong b nt n.

4- Cng tc: L kh c ng ct bng tay hoc bng tc ng c kh mch in h p.

- Khi dng cng tc phi ch in p,

dng in ca tip im cng tc. C

cc loi cng tc dng cho mch ng

lc (thng dng cng sut nh) cn

a phn cng tc ch dng trong mch in iu khin, cu to ca cng tc thng c tip im ng v tip im tnh kiu n gnh, c c cu tr lc l xo tc ng nhanh

- C 2 loi cng tc chnh l: Cng tc xoay (thng mi gc xoay l 450) v cng tc hnh trnh (kiu gt v kiu t ).

- Cng tc hnh trnh c dng rt nhiu trong thc t iu khin chuyn ng in theo v tr, hnh trnh hoc bo v, m bo an ton hnh trnh chuyn ng ca thit b.

5- ptmt: L kh c in bo v c th ct mch t ng khi c s c nh: Qu ti, ngn mch, qu p...

- Nguyn l ca p t mt l

da vo nguyn l in t (bo

v cc i) v nguyn l nhit (bo v qu ti)

- Trong thc t hay gp p t mt va c bo v cc i va c bo v ct nhanh.

- Khi s dng ch chn ng gi tr in p, dng in nh mc ca p tmt.

6- Cng tc t: L kh c in iu khin t xa dng ng ct cc mch in ng lc mch p ti 500V v dng in ti hng ngn am pe.

+ Cu to ca mt cng tc t gm.

- Cun dy li thp ( cun ht)

- H thng cc tip im(ng lc

v iu khin)

- Li thp v l xo phn.

+ Ch khi s dng: in p cun dy

v dng in in nh mc ca cng

tc t phi ph hp vi ti ngoi ra cn

phi tnh n tn s ng ct (tn s

thao tc) ca n. Trong s dng hay xy

ra trng hp vng ngn mch ca cng

tc t b t dn n lc ht gim ( pht

ra ting ku r r mch t ng thi

c th gy nh la, pht nng tip im

ng lc ( nu khng s l s dn ti s c ( s l hn li vng ngn mch.

7- R le nhit: L phi dng bo v mch in, thit b khi b qu ti.

- Nguyn l ca r le nhit: Da trn s gin n kch thc ca vt th di tc dng ca nhit.

- Cu to gm: 1 thanh lng kim (2 thanh kim

loi c h s gin n nhit khc nhau c

ghp cht vo nhau) v 1 ngun nhit

t nng n (trc tip, gin tip, hn hp)

khi b t nng n s un cong v tc ng ng m ly.

- Do c qun tnh nhit ln nn khng bo

v c ngn mch cng nh qu ti ln

trong thi gian ngn.

- Trong thc t thng ch dng nh

mc ca r le nhit bng dng in nh

mc ca thit b v dng in tc ng

c ch nh l: Itd =1,2(1,3 In.

- Mt ch quan trng l khi nhit mi trng xung quanh r le nhit tng cao n s lm vic sm hn ( Cn chnh nh li dng tc ng.

8- Rle thi gian: L loi rle to tr u ra ngha l khi u vo c tn hiu iu khin t sau mt thi gian no tip im rle mi tc ng ng hoc m (T=vi giy(vi gi).

- Trong thc t hin nay a phn ta gp rle thi gian kiu in t n c u im l chnh xc, nh gn v tin cy cao.

- Khi s dng ch : in p cun dy,

v kh nng ng ct ca tip im (vi

rle thi gian kiu in t cn cho php

ta chn n v o l: S, M,H do cn

ch tm hiu k i vi mi loi khi gp trong thc t).

9- Rle trung gian: Dng khuych i cc tn hiu iu khin.

- Rle trung gian thng l cc rle in

t c nhiu cp tip im.

- Khi dng cn ch ti in p cun ht

v dng in ca tip im cng nh s

ln ng ct.

b/ Cc my in thng dng:

1- ng c khng ng 3 pha:

- Nguyn l: Da trn hin tng cm ng in t, khi cho dng 3 pha vo dy qun 3 pha Stato t lch nhau 1200 trong khng gian th s to nn mt t trng quay. T trng quay qut qua thanh dn ca Roto nn to ra sc in ng cm ng v cc thanh dn c ni ngn mch nn sinh ra dng in. Dng in ny nm trong thi gian ( b tc dng ca lc t to ra m men lm Roto quay.

- Cu to: Gm 3 thnh phn l chnh:

- Stato (phn tnh) gm c li thp, v my.

- Dy cun 3 pha (t trong cc rnh

ca li thp Stato).

- Roto (phn quay) gm c li thp roto

v trc quay.

- c tnh c ca CKB nh hnh v

trong ta chia lm 2 on.

- on AK thng, cng l on lm vic

n nh.

- on BK l on lm vic khng n nh.

- Mmen ti hn CKB t l vi bnh

phng in p t vo dy qun Stato M ( U2- Dng in m my ca CKB rt ln Imm = (5 ( 7) Im tu thuc vo cng sut ng c v h truyn ng do cn phi ch hn ch dng khi ng. Trong thc t ngi ta hay s dng cc phng php: i ni Y - ( ; Gim in p t vo dy qun Stator ; Tng in tr Rf mch roto m my ng c khng ng b cng sut ln.

2- ng c in mt chiu:

- Nguyn l: Da vo hin tng cm ng in t.

- Cu to:

- Stato (phn cm) c qun cun dy trn cc t (cun kch t ).

- Roto (phn ng)- C gp.

- Chi than.

- ng c in mt chiu c rt nhiu loi, kch t c lp, song song, ni tip v hn hp. Ta ch xt ng c kch t c lp (ngun kch t c lp vi ngun phn ng).

- c tnh c rt cng v tc t l thun vi in p.

IV Cc s khng ch:

1- S khng ch ng c khng ng b:

a- Hu ht cc ng c (khong 97%) trong cng ty nhm Sng Hng c khng ch bng s khi ng trc tip, khng o chiu.

QF: p t mt

KM: Cng tc t

FR: R le nhit

M: ng c KB.

FU: Cu ch

SB1: Nt bm Stop

SB2: Nt bm START

HL1: n xanh bo ngun

HL2: n bo chy.

- Vn hnh: ng QF n xanh HL1 sng, bo c ngun mch in sn sng lm vic.

- n nt khi ng SB2 cun KM c in, tc ng ng mch lc cp in cho ng c M, ng thi ng tip im t duy tr ( n HL2 sng bo ng c bt u hot ng, cng lc n HL1 b ct ngun ( tt.

- ng c c bo v qu ti bng rle nhit FR, khi c qu ti (I = 1,25Im) rle nhit FR tc ng m im thng ng FR ct in cun dy cng tc t KM ( ng c b ct ra khi li, sau khi s l s c phi n nt phc hi rle nhit th mch mi hot ng li c.

- Mch ng lc c bo v ngn bng p tomt QF.

- Mch in iu khin c bo v ngn mch bng cu ch FU.

Mch in trn c dng cho ton b h bm ho cht, qut gi, bm nc phn xng xy ho v cn p.

b- S iu khin ng c KB dng phng php khi ng Y-(:

Cc ng c cng sut ln t 15 ( 100KW nh ng c qut gi l sn phm, bm du thu lc cc my p, qut khi phn xng c u dng mch khi ng Y - ( m my nhm gim dng K v bo v ng c. S ny ch p dng c cho cc ng c m ch lm vic bnh thng n ni (.

+ S :

- Nguyn l lm vic: ng p tmt AT, n nt M cng tc t K, rle thi gian T v cng tc t Ky c in, dy qun Stato c ni hnh Y qua cc tip im ca Ky , ni vo li qua cng tc t K ( ng c m my vi in p pha gim ln so vi nh mc.

- Sau mt thi gian chnh nh r le thi gian T tc ng tip im T1 m ra ct in cng tc t Ky, tip im T2 ng, tip in cho cng tc t K( ( ng c c ni (. lm vic in p nh mc, qu trnh m my kt thc.

- Khi n nt D ( ng c c ct khi li v dng t do.

- S c bo v ngn mch bng AT, qu ti bng RN. Ngoi ra trnh xy ra trng hp K( v Ky ng in ng thi gy ra ngn mch 3 pha, trn s c kho cho v in bng cc tip im ca K( v Ky , T.

2- S khi my xy ho.- Cc my xy ho phn

xng xy ho l cc thit

b bin i xoay chiu -

mt chiu cng nghip cng

sut ln rt phc tp, n

c vin nghin cu in

Qung Chu - T.Quc nghin

cu v sn xut phc v

cho nghnh cng nghip sn

xut nhm. Chc nng nhim v ca my l bin ngun in xoay chiu 3 pha 380V ca li thnh ngun in mt chiu c th iu chnh c t 0 ( 25VDC vi dng ti 0 ( 10000A, y l mt thit b kh hin i, k thut iu khin tng t kt hp vi k thut s nn tin cy rt cao, an ton hiu qu. Sau y ta ln lt xem xt s khi ca my.

- C th chia my lm 4 khi chnh vi chc nng nhim v ca tng khi nh sau:

+ Khi bin i in p xoay chiu- xoay chiu AC/AC: C nhim v bin i in p AC 3P - 380V thnh in p thch hp a vo bin p T. Khi ny dng cc phn t chnh lu c iu khin Tiristo v chu s iu khin ca b iu khin CC, khi AC/AC

+ Khi bin p T: C nhim v cch ly mch th cp c in p thp vi mch s cp c in p cao m bo an ton cho con ngi, ng thi cn cn c nhim v h p v phn pha m bo cung cp c mt ngun dng xoay chiu ln theo yu cu.

+ Khi chnh lu xoay chiu - mt chiu AC/DC: C nhim v bin i dng xoay chiu a ra th cp bin p T thnh dng 1 chiu a ra b xi ho. Khi ny dng cc it chnh lu cng sut ln.

+ Khi iu khin CC: C nhim v to ra cc xung iu khin iu khin khi AC/AC. khi CC nhn cc tn hiu tn hiu t; ng b, phn hi (dng p) v ri tng hp li thnh cc xung iu khin p ng theo yu cu ca cng ngh.

+ Ngoi ra my cn c cc chc nng bo v kh hon chnh bo m an ton, cho con ngi cng nh thit b nh bo v ngn mch dng t t mt AT, bo v mt pha dng mch in t, bo v qu nhit, bo v p thp...

- Cc ch khi vn hnh:

Trc khi vn hnh, ng in cn kim tra xem xt in c pha, ng pha khng, h thng qut thng gi c lm vic khng? Sau vn chit p iu khin v v tr khng, la chn ch lm vic (n p hay n dng v thi gian xy ho) ri mi bt cng tc my, sau t t vn chit p ln, nhn ng h A, V theo di xem ng v tr s dng, p cn t cha. My s t ng lm vic theo gi t t dng, p v thi gian yu cu khi kt thc my s pht ci bo hiu v t ng dng my. Ngi vn hnh tt cng tc v xoay chit p v v tr khng chun b cho m sn xut tip theo.

Trong khi lm vic khng nn tt m cng tc hoc iu chnh chit p lin tc, n c th gy s c lm h hng thit b v mch c dng lm vic ln, cm khng ln khi ng ngt nhiu d gy qu p ni b ph hng thit b.

3- S khi my nhum mu:

- Thit b nhum mu: C chc nng bin ngun 3P 380V 50Hz thnh ngun xoay chiu bin thin theo quy lut p ng yu cu cng ngh. in p v dng in u ra c th thay i t 0 ( 25V, dng in t 0 ( 2000A . my c th chia lm 3 khi sau:

+ Khi ng ct v bo v: Bao gm t t mt AT v b Tiristo c nhim v ng ct khng tip im. Khi ny chu s iu khin ca b iu khin CC.

+ Khi iu chnh in p xoay chiu-xoay chiu V - R : C nhim v cch ly mch th cp vi mch s cp (li in) m bo an ton, ng thi iu chnh in p ra theo ng chu trnh cng ngh. Khi ny chu s iu khin ca mch CC.

+ Khi iu khin CC : nhn tn hiu t, tn hiu phn hi v ri gia cng thnh tn hiu iu khin iu khin 2 khi ON/OFF, V R sao cho n cho ra c tnh in p, dng in ng theo yu cu ca cng ngh.

+ My nhum mu cng c cc loi bo v mt pha, qu nhit nh my xy ho.

+ Khi vn hnh cng cn tun theo cc ch nh my xy ho im khc bit l thi gian mt chu trnh nhum rt ngn nn vic iu chnh thi gian, in p phi qua thc t vn hnh mi c kinh nghim c.

4- S khi cc thit b gia nhit:

Trong dy chuyn sn xut nhm c s dng rt nhiu cc thit b gia nhit nh cc l phi, khun, sn phm, thng p l nit khun... tuy rt a dng v chc nng, cng sut kiu dng nhng chung quy li n u tun theo quy lut iu khin nhit dng trong cng nghip. N c s d khi nh sau:

- Khi bo v v ng ct AT + C. C chc nng bo v mch khi qu ti, ngn mch (dng ptmt v cu ch) ng thi ng ct ngun cung cp cho h thng my do phn b u trong khng gian l v dng in 3 pha 380V. Tu theo cng sut v nhit m cc dy c ng knh khc nhau cng nh cch u ni khc nhau.

- Khi iu khin C: Nhn cc tn hiu kim tra t cc can o nhit v x l, so snh vi nhit t yu cu ri a ra cc lnh iu khin ti khi ng ct iu chnh qu trnh gia nhit. Khi iu khin nhit l mt mch in t phc tp nhng cng ngh hin nay ch to thnh cc m un mch nh gn v hon chnh (nh XTM, XTMA... ca Trung Quc) ch vic dng kt hp vi can o nhit l ta c mt b phn iu khin hon thin.

- Ngoi cc khi chnh trn th tu theo tng loi l ta c thm cc thit b ph tr nh h thng qut i lu, phn gi h thng m thi gian gia nhit, h thng ng h t ghi chu trnh gia nhit...

- Trong vn hnh: Sau khi t nhit , thi gian gia nhit ta bt cng tc my s t ng lm vic theo chu trnh nh sn, khi t yu cu my s pht tn hiu (chung ku, n bo) ngi vn hnh bit.

5- Cc my p - My lnh v cc thit b ph tr khc:

Cc my p l mt h bn t ng c s dng lp trnh PLC rt phc tp, ngi vn hnh phi trc tip hc cng ngh, cch vn hnh ti my, y khng th a ra c nguyn l vn hnh v n kt hp nhiu h thng iu khin in t, in, thu lc, kh nn...

- Cc my lnh v mt s thit b ph tr khc do yu cu cng ngh cng nh quy tnh vn hnh phc tp nn c nh sn xut my thit k khp kn, ngi vn hnh ch vic n cng tc l my hot ng. Mi s iu chnh do k thut vin c o to chuyn mn m nhim nn y khng gii thiu.

V- An ton in trong sn xut:

Theo phn loi cc x nghip cng nghip v an ton in th dy chuyn sn xut nhm thanh nh hnh c xp loi nguy him v in v cc l do sau:

- Mt b tr thit b dy c, mi trng sn xut nng m t, c hi ho cht, bi... do vy mi ngi cn phi c hun luyn chu o cn thn v an ton in trnh xy ra cc tai nn, s c ng tic cho con ngi v thit b.

Phn ny s trnh by cc vn c lin quan n an ton in trong sn xut nh:

1/ Tc dng (tc hi) ca dng in i vi c th con ngi.

2/ Nhng nguyn nhn v yu t ch yu gy nn cc tai nn v in.

3/ Cc bin php an ton khi s dng sa cha in (c nu y cc bin php t chc cng nh cc bin php k thut).

4/ Cc phng php cp cu ngi b in git.

Cc vn trn c trnh by di dng a ra cu hi v tr li cc hc vin c th r rng hc tp, nh v vn dng c trong thc t.

cng:

Cu 1: Nu hiu bit ca ng ch v vn an ton in?

Cu 2: Nu tc dng ca dng in i vi c th con ngi? Nhng nguyn nhn v yu t ch yu gy nn nhng tai nn v in trong thc t.

Cu 3: Cc bin php an ton khi dng in?

Cu 4: Cc bin php cp cu ngi b in git?

p n:

Cu 1: Dnh cho hc vin ( nhm kim tra nhn thc).Cu 2: Nu tc dng ca dng in i vi c th con ngi? Nhng nguyn nhn v yu t ch yu gy nn nhng tai nn v in trong thc t.

* Tc dng ca dng in i vi c th con ngi: Trong thc t cc tn thng v in th hin tng b in git l nguy him nht v dng in tc dng n h thn kinh gy nn s ngng tr ca b my h hp v tun hon, lm nhp tim b ri lon h thng c bp b kch thch gy co qup, m hi... Ngoi ra dng in cn gy tc dng trn thng do lm vic t trn cao b in git ng xung hoc lm b thng do tc dng nhit ca dng in h quang.

- Mc nguy him khi b in git tu thuc vo tr s ca dng in qua c th con ngi.

- Vi ngun in c tn s 50 ( 60Hz th dng in gy chn thng ti c th c tr s t 20 ( 25mA. Cn t 50 ( 80mA th gy ri lon c th cn t 100mA (0,1A) th tim s ngng p sau 3 ( 5 giy.

- Vi dng in xoay chiu 50 ( 60Hz th vi cng dng in t 20 ( 25mA th tay kh ri vt mang in.

- Vi cng dng in t 50 ( 80mA th h h hp b t lit, nhp tim ri lon c bp co qup cn vi dng in trn 100mA tim s ngng p v dn n t vong trong thi gian rt ngn.

* Nhng nguyn nhn v yu t ch yu gy nn tai nn v in trong thc t:Cc nguyn nhn: Tai nn v in xy ra rt a dng do nhiu nguyn nhn nhng chung quy li th 4 nguyn nhn ch yu sau:

1/ Do con ngi v chm vo phn mang in. Trong thc t nguyn nhn xy ra tai nn do nguyn nhn ny khng nhiu bi v cc vt mang in c bo v che chn v bn thn con ngi cao cnh gic ch phng.

2/ Do con ngi chm vo cc phn kim loi bnh thng m khng c in nhng v in tr cch in b h hng nn tr thnh c in. Nguyn nhn ny thng gy ra nhiu tai nn v in, bi v ngi vn hnh thng xuyn tip xc vi cc phn khng mang in nh v my, li bo v, khung my... nu cch in b h hng th in r r ra v my, li cch in... ( hin tng chm v) hin tng ny rt kh pht hin ra.

3/ Do h quang in: i vi mng in cao p mc d cha tip xc vi phn mang in nhng do khong cch khng m bo (tc l khng m bo khong cch an ton quy nh) c th gy ra h quang in. H quang in c th pht sinh do thao tc khng ng quy trnh, quy phm... trong thc t nguyn nhn ny khng nhiu lm bi v c quy trnh, quy phm cht ch, mt khc c thit b che chn v dp h quang.

4/ Do in p bc: Khi ngi bc vo t hoc vo thao tc sn my bng vt dn in nh st, thp... c dng in chy qua (r r, dy in t ...) th gia hai chn ngi c mt in p bc. Trong phm vi 20m l vng nguy him, 68% in p ri trong khong 8m. Khi ngi chm vo vt mang in th gia tay v chn ngi c mt in p gi l in p tip xc.

* Cc yu t ch yu:

1/ Tr s dng in qua ngi: Ngi ta thy rng vi dng in xoay chiu 50Hz ch an ton vi con ngi nu dng in qua con ngi nh hn 10mA. Cn vi dng in 1 chiu th tr s an ton nh hn 50mA.

2/ Thi gian tip xc vi dng in: Thi gian tip xc cng lu th cng nguy him v in tr ca ngi gim do tc dng kch thch ca dng in.

3/ ng i ca dng in: Ngi ta thng ly phn lng dng in qua tim (phn trm dng in qua tim). nh gi mc nguy him v ngi ta th nghim tng kt c phn lng dng in qua tim vi cc ng i khc nhau ca dng in. Nguy him nht l t tay tri ti chn.

4/ Tn s ca dng in: Tn s dng in c nh hng nhiu ti tai nn v in, ni chung tn s cng cao th cng t nguy him. Nguy him nht l dng in c tn s gn tn s dng in cng nghip.

5/ Mi trng: Nhit bi v c bit l m c nh hng ln ti in tr cch in ca ngi, n lm thay i in tr ca ngi dn n lm thay i tr s ca dng in qua ngi.

Cu 3: Nu cc bin php an ton khi dng in:* C nhiu bin php an ton bo v an ton khi vn hnh, s dng, sa cha cc thit b in. Tuy nhin phi nh rng khng c mt bin php no m bo an ton tuyt i v bin php bo v an ton ch yu l yu cu cng nhn , th sa cha... khi vn hnh s dng cc thit b in u phi nghim chnh tun theo cc quy trnh quy phm an ton ra. Sau y l 2 bin php ch yu:

1/ Cc bin php t chc:

- Chn ngi lm vic c sc kho c kin thc chuyn mn v bit s dng thnh tho cc quy trnh, quy phm an ton.

- T chc lm vic: Tt c cc cng vic tip xc vi dng in u c ghi trong phiu cng tc. Phiu cng tc ghi cc ni dung ch yu sau:

+ a im lm vic.

. + Ni dung cng vic.

+ Thi gian lm vic.

+ Cc ch an ton.

- T chc kim tra: Tt c cc cng vic tip xc vi mch in mi ni u phi c 2 ngi: 1 ngi lm vic cn 1 ngi ng canh phng kim tra. Ngoi ra cn phi s dng cc biu bo ro chn...

2/ Cc bin php k thut:

- phng tip xc vi dng in: Tt c cc thit b in bao gi cng c in tr cch in ngn cch gia phn mang in v phn khng mang in m bo khi tip xc vi dng in qua ngi trong phm vi cho php. Vi mng in p phi c m bo yu cu cch in l 1000(/V. Vi in p 220V th in tr cch in phi ( 0,2M(. Vi in p 380V th in tr cch in phi ( 0,38M(. m bo an ton bao gi cng phi kim tra cch in ca thit b trc khi s dng.

- Ngoi ra khi sa cha tip xc vi mch in cn phi che chn (dng li hoc hng ro), quy nh cc khong cch an ton, treo cc biu bo, phng tip xc vi b phn bnh thng khng mang in nhng v cch in h hng dn n c in, vi cc trng hp ny cch phng tt nht bng cch ni t an ton. Tc dng ca dy ni t an ton l thot dng in vo trong t v gi mc in th thp trn cc vt c ni t.

Tip in bo v: Tc dng ch yu ca tip in bo v l h thp in th ca phn kim loi khng mang in khi c hin tng chm v. Ngi ta thc hin bo v chm v bng cch ni cc phn kim loi khng mang in ca thit b vi t hoc dy trung tnh ca mch, nh th khi hin tng chm v xy ra s tr thnh s v ngn mch mt pha v cc thit b bo v s tc ng ct ri thit b hoc phn chm v ra khi mch in.

Cu 4: Cc phng php cp cu ngi b in git:

* Cc phng php tin hnh cp cu ngi b in git nh sau:

- Nhanh chng ct ly ngi b in git ra khi phn mang in v nhanh chng ct in dn ti nn nhn.

- Dng vt khng dn in ht dy in ra khi ngi b nn , dng gng tay, ko o v ngi b in git ra khi vt dn in. c th dng vt cch in ct t dy dn.

- Sau khi nn nhn c tch ra mch in m cc c quan h hp, tun hon cn hot ng th tin hnh a nn nhn ti ni thong kh ni rng qun o. trong trng hp cc c quan tun hon ngng hot ng th phi tin hnh h hp nhn to, h hi thi ngt, xoa tim ngoi lng ngc ... sau nhanh chng a nn nhn n bnh vin, trm x hoc ni cp cu gn nht.

Vic cp cu ngi b in git l mt cng vic khn cp nn phi tin hnh cng nhanh cng tt dng tu theo hon cnh m phi c ng dng phng php cp cu cho thch hp v phi ht sc kin tr bnh tnh.

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